GB1593923A - Superconductor coils - Google Patents

Description

PATENT SPECIFICATION

( 11) 1 593 923 ( 21) Application No 8408/78 ( 31) ( 33) ( 22) Filed 2 Mar 1978 Convention Application No 2709300 ( 32) Filed 3 Mar 1977 in Fed Rep of Germany (DE) ( 44) Complete Specification Published 22 Jul 1981 ( 51) INT CL 3 HO O F 5/00 7/22 ( 52) Index at Acceptance Hi P l A 1 2 E ( 54) SUPERCONDUCTOR COILS ( 7 1) We, S I E MEN S AKTIENGESELLSCHAFT, a German company, of Berlin and Munich, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow-

ing statement:-

The invention relates to superconductor coils.

Magnet field coils, or windings, comprising conductors incorporating a superconductor material may advantageously be used for generating strong magnetic fields In use such superconductor conductors are cooled by a cooling agent, generally liquid helium, to a temperature below the "critical" temperature of the superconductor material, as a result of which the ohmic resistance of the superconductor material disappears almost completely As a result of the reduction in the energy required by field coils employing such conductor magnets formed with such conductors have an advantage over conventional magnets having field coils of material having only normal electric conductivity, such as copper, in that they can be used to generate stronger magnetic fields, i e steeper magnetic gradients.

In order to obtain very high magnetic fields or steep magnetic gradients, the effective current densities in the superconductor conductors of a magnet employing field coils with superconductor material must usually be made correspondingly high In such cases, the super-conductor conductors may need to be loaded to near their critical current limit The conductors need special protection against mechanical instability, e.g as a result of motion If, for example, a superconductor conductor in a field coil is able to move in response to external forces, e.g Lorentz forces, the resulting friction or kinetic energy, converted into heat, may heat the conductor, or a part thereof, to above its critical temperature so that it becomes normally conducting.

In order to prevent such mechanical instability and resultant heating of conductors, the individual conductors of a superconductor field coil or winding can be impregnated in vacuo with a material which subsequently hardens and thus holds the conductors in position Vacuum impregnation of this kind is particularly advantageous for magnet field coils made of thin, very brittle or fragile superconductor conductors, such as Nb 3 Sn or V 3 Ga conductors, which are heat-treated "in situ" In superconductor magnets in which the field coils are heat-treated "in situ", the coils are first wound from composite conductors made of the individual elemental components of a superconductor compound to be formed in the finished conductors, before the elemental components have been reacted together.

Next, the field coils made of the composite conductors are heat-treated, as a result of which the elemental components in the composite conductors diffuse together and form the desired superconductor compound This method can avoid unacceptable distortion of brittle superconductor conductors which might otherwise occur when the field coils are wound.

Two methods of vacuum impregnation have been proposed In a first method, proposed in German Offenlegungsschrift 22 56 921, additional moulds or "ingot moulds" are required, in which the magnet field coils are covered with impregnating agent In this method, relatively thick layers of impregnating agent inevitably form at the ends and on the rest of the surface of the field coils Thick layers of impregnating agent adversely affect the cooling of the superconductor field coil and, more particularly, they may contract considerably during cooling and thus subject some conductors, e g leads ( 19) 1 593 923 to external supply contacts, to forces which may break individual filaments of a conductor or an entire conductor Excessively thick layers of impregnating agent can be removed, but this takes time and there is a risk of damaging conductors In addition, with the method proposed above, new moulds are required if the dimensions of magnets being fabricated are changed, and this can be relatively expensive.

Moulds are avoided in a second proposed method of a vacuum-impregnating the conductors of a superconductor field coil In the second proposed method, special formers are required together with a winding support on which the superconductor field coil is wound during manufacture Such a former is proposed, for example, in German Gebrauchsmuster 75 33 199 In this second method there is employed a hollow cylindrical winding support with respective ringform flanges at its opposite ends A winding space is formed around the support between the opposite end flanges The two end flanges have bores therethrough extending parallel to the axis of the support by means of which the winding space is connected at its opposite ends to respective annular collecting ducts formed outside the flanges.

Each collecting duct is formed by a recess in a cover plate, which is required in addition to the winding support, and which abuts the external face of the end flange concerned in vacuum-tight manner After the conductors have been wound on the support in the winding space, and the resulting set of conductors have been provided with an external jacket impervious to the impregnating agent, an impregnating agent can be supplied through a supply pipe to the collecting duct at one end of the support and thence via the axial bores in the end flange concerned to the voids between the individual conductors in the field coil At the opposite end of the support, the impregnating agent is similarly conveyed through axial bores and the collecting duct formed at that end and out through a cover plate and discharge pipe In this second method also, excess layers of impregnating agent inevitably form at the flanges The excess layers have to be removed.

The method using moulds is suitable for impregnating field coils previously provided with contacts for receiving current from an external supply, but this is impossible when using formers as employed in the second method, since the cover plates on the flanges of the winding support leave no room for contacts Contacting therefore, is possible only after the impregnation is complete and the cover plates have been removed This makes it impossible to use the second method, for example, for Nb 35 N 1 or V 3 Ga field coils heat-treated "in situ", since in these cases the contact leads, owing to the relatively small permissible bending radii for conductors of such coils, usually have to be preformed and laid before diffusion heat-treatment and must not be moved subsequently to any substantial extent, since the conductor materials are sensitive to bending In the second method, as in the first, alteration of the dimensions of the field coils to be formed is relatively expensive since new cover plates are required.

According to one aspect of the present invention, there is provided a method of manufacturing a superconductor coil, wherein a superconductor coil winding assembly is formed around a central axial portion of a winding support, in a winding space defined between respective end flanges of the winding support that project radially outwardly from the central axial portion at opposite ends thereof, the winding assembly being surrounded laterally by peripheral sealing means and having opposite axial end faces adjacent respectively to the said end flanges, with an end space between one axial end face and the adjacent end flange, in which end space an annular body is provided, around the central axial portion, an annular duct in that space being defined between the annular body therein and the end flange concerned, and the annular body being formed with axial ducts, and wherein impregnating agent is passed into the winding assembly at the said one axial end face thereof by way of the annular duct and the axial ducts in the annular body.

According to another aspect of the present invention there is provided a superconductor coil, comprising a superconductor coil winding assembly provided around a central axial portion of a winding support in a winding space defined between respective end flanges of the winding support that project outwardly from the central axial portion at opposite ends thereof, wherein the winding assembly is surrounded laterally by peripheral sealing means, has opposite axial end faces adjacent respectively to the said end flanges with an end space between one axial end face and the adjacent end flange, and is impregnated with impregnating agent, the coil having ducts, for the passage of impregnating agent to the winding assembly in the manufacture of the coil, provided by an annular body having axial ducts therethrough and disposed around the central axial portion in the end space to define an annular duct between the annular body and the end flange concerned.

The present invention can be well suited to superconductor field coils having thin, brittle, fragile superconductor conductors, for example conductors incorporating Nb 3 Sn or V 3 Ga superconductor compounds 1 593 923 formed by "in situ" heat treatment and which need to be fitted with contacts prior to the heat-treatment.

A method embodying the present invention can be put into effect without the necessity for expensive aids such as moulds or field cover plates Thereby changes in the size of coils to be manufactured do not necessarily entail expensive re-equipping.

Further, by the use of a method embodying the present invention the formation of thick layers of impregnating agent at the surfaces of a field coil can be avoided, thereby reducing the amount of finishing treatment required after impregnation.

In preferred methods embodying the present invention a space is left between an axial end face of the coil winding assembly and the end flange adjacent thereto at each axial end of the winding assembly, and annular ducts in the respective spaces are used for distribution and collection of impregnating agent.

Such methods of manufacturing coils embodying the present invention can have an advantage in that the manufacturing cost of impregnating the field coil may be relatively low For example, where a prefabricated winding support is employed, no additional operations are required for forming the spaces at axial ends of the winding assembly, which are readily adapted to the proposed dimensions of the coil being made The difficulties caused by thick layers of impregnating agent in the previously proposed processes can be avoided, since in practice the impregnating agent fills only the voids in the winding space bounded by the winding support and the outer periphery of the coil winding assembly Since no additional devices are required (such as cover plates) on the exterior faces of the end flanges, previously-contacted field coils, more particularly Nb 3 Sn field windings heat-treated "in situ", can be impregnated.

The finishing treatment of an impregnated coil is mainly restricted to the removal of the supply or discharge pipes for the impregnating agent.

An annular body is disposed in the space left between an axial end face of the coil winding assembly and the end flange adjacent thereto in further preferred embodiments of the present invention The annular duct for impregnating agent is formed between the body and the end flange The body has apertures therethrough so that impregnating agent can pass between the annular duct and the axial end face of the coil winding assembly The annular body may be formed from perforated plate Suitable perforated plate of a variety of nonmagnetic materials, such as VA steel, is commercially available and can readily be formed into an annular shape as required.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing which shows a diagrammatic cross-section through a superconductor coil embodying the present invention for the manufacture of which a method embodying the present invention has been employed.

The drawing shows a former having a winding support 2 comprising a centre portion 4, which is rotationally symmetrical around an axis 3, e g a tubular or hollow cylindrical portion The tubular centre portion has connected at its opposite respective ends radially-outwardly projecting end flanges 5 and 6 The end flanges are circular in form Centre portion 4 and flanges 5 and 6 can be formed as a one-piece member, e.g on a lathe A coil winding assembly 7 having a set of coil windings for forming a field coil 8 is formed on the support 2 comprising parts 4 to 6 Windings formed, for example by a set of Nb 3 Sn conductors heat-treated "in situ" can be employed The coil winding assembly 7 has its opposite end faces covered by layers 9 in the illustrated arrangement Layers 9, which are mainly for insulating the windings from adjacent metal parts, are made for example of individual strips of textile or glass fibre and are permeable by to the impregnating agent to be employed If required, layers 9 can be omitted The lateral outer periphery of winding assembly 7 is covered in sealingtight manner by a jacket, e g a bandage 10.

As shown in the drawing, bandage 10 can cover the assembly 7 and the end flanges 5 and 6.

Flat, annular spaces 12 and 13 are disposed between flanges 5 and 6 respectively and the end faces of the winding assembly 7 (which end faces may be covered by layers 9) Bandages 10 may serve to close the annular spaces 12 and 13 laterally The size of spaces 12 and 13 depends on the given dimensions of coil 8 and support 2 Annular discs 14, having axial bores 15 (bores extending parallel to axis 3), for example constituted by annular perforated plates, are disposed each in a radial plane (a plane extending radially from axis 3) in respective spaces 12, 13 (parallel to the end flanges).

Advantageously the perforated plates are made of a non-magnetic material such as a special steel or a plastics material Since the axial thicknesses of the plates are less than the axial dimensions of spaces 12 and 13 and one side of each perforated plate is adjacent a respective layer 9 (if present) covering an end face of the coil winding assembly, respective flat annular ducts or channels are formed between the plates and flanges 5 and 6 In the drawing, a distribution duct associated with the lower (as seen in the drawing) 1 593 923 flange 5 of support 2 is denoted by 16, whereas a collection duct associated with the upper flange 6 is denoted by 17.

Advantageously, the sides of the respective plates 14 which face ducts 16 and 17 are formed with supporting projections 19 which abut flanges 5 and 6 respectively This prevents the plates 14 from moving in the ducts 16 and 17 and, more particularly, protects the plates, which are usually relatively thin, from being deformed by the pressure of coil winding assembly.

As soon as the coil winding assembly has been sealed in a vacuum-tight manner, e g.

by bandaging, and has been tested for sealing-tightness, it can be impregnated in vacuo with a liquid impregnating agent, e g.

a curable synthetic resin For this purpose, as indicated by an arrow 20 in the drawing, impregnating agent is first introduced into the lower duct 16 (the distribution duct) through a bore 21 in the lower flange 5 It flows through the axial bores 15 of the adjacent plate 14 and between the strips of layer 9 into voids between the conductors of coil winding assembly 7 The impregnating agent eventually reaches the top of the coil winding assembly and passes through the gaps between the strips of layer 9 and the axial bores 15 of the top plate 14, flows into the top duct 17 (the collection duct) and is discharged therefrom, as indicated by an arrow 22, through an outflow bore 23 in the upper flange 6.

Consequently, in the method embodying the present invention illustrated by reference to the drawing, the introduction of impregnating agent does not require additional devices such as cover plates, which have to be externally secured to the flanges, but its effected directly by means of supply and discharge systems incorporated in the flanges.

Nozzles for the supply and discharge pipes for the impregnating agent are secured e g by screwing, to bores 21, 23 in flanges 5, 6 The drawing shows only an outlet nozzle 25 for the discharge pipe.

After the voids in the field coil have been filled with impregnating agent and the agent has hardened, it is necessary merely to remove the supply and discharge lines, without further finishing treatment of the coil.

The drawing also shows a contact plate 26 on the top flange 6, to which contact elements can be secured between the conductors of winding 8 and the required current supply and return leads The drawing shows a contact element 27 in detail on plate 26.

Claims (18)

WHAT WE CLAIM IS:-

1 A method of manufacturing a superconductor coil, wherein a superconductor coil winding assembly is formed around a central axial portion of a winding support, in a winding space defined between respective end flanges of the winding support that project radially outwardly from the central axial portion at opposite ends thereof, the winding assembly being surrounded laterally by peripheral sealing means and having opposite axial end faces adjacent respectively to the said end flanges, with an end space between one axial end face and the adjacent end flange, in which end space an annular body is provided, around the central axial portion, an annular duct in that space being defined between the annular body therein and the end flange concerned, and the annular body being formed with axial ducts, and wherein impregnating agent is passed into the winding assembly at the said one axial end face thereof by way of the annular duct and the axial ducts in the annular body.

2 A superconductor coil, comprising a superconductor coil winding assembly provided around a central axial portion of a winding support in a winding space defined between respective end flanges of the winding support that project outwardly from the central axial portion at opposite ends thereof, wherein the winding assembly is surrounded laterally by peripheral sealing means, has opposite axial end faces adjacent respectively to the said end flanges, with an end space between one axial end face and the adjacent end flange, and is impregnated with impregnating agent, the coil having ducts, for the passage of impregnating agent to the winding assembly in the manufacture of the coil, provided by an annular body, having axial ducts therethrough and disposed around the central axial portion in the end space to define an annular duct between the annular body and the end flange concerned.

3 A superconductor coil as claimed in claim 2, with a further end space between the other axial end face of the winding assembly and the end flange adjacent thereto, having a further annular duct, for the passage of impregnating agent from the winding assembly in the manufacture of the coil, in the further end space.

4 A superconductor coil as claimed in claim 3, having ducts, for the passage of impregnating agent from the winding assembly in the manufacture of the coil, provided by a further annular body having axial ducts therethrough and disposed around the central axial portion in the further end space to define the further annular duct between the further annular body and the end flange concerned.

A superconductor coil as claimed in claim 2, 3 or 4, wherein the or each said annular body is formed from a perforated plate.

6 A superconductor coil as claimed in 1 593 923 5 claim 2, 3, 4 or 5, wherein the or each annular body has supporting projections which bear on the adjacent end flange.

7 A superconductor coil as claimed in any of claims 2 to 6, wherein the or each axial end face is covered by a layer of electrical insulating material permeable by the impregnating agent.

8 A superconductor coil as claimed in any one of claims 2 to 6, wherein the or each said annular body bears directly on a layer of electrical insulating material that is permeable by the impregnating agent and covers the said axial end face that is adjacent to the annular body concerned.

9 A superconductor coil as claimed in any one of claims 2 to 8, wherein the said central axial portion has the form of a hollow cylinder and the said end flanges are circular in form.

A superconductor coil as claimed in any one of claims 2 to 9, wherein the coil winding assembly comprises superconductor windings of Nb 3 Sn or V 3 Ga, formed "in situ" by heat treatment.

11 A superconductor coil substantially as hereinbefore described with reference to the accompanying drawings.

12 A method as claimed in claim 1, wherein some of the impregnating agent passes out of the winding assembly, at the other axial end face thereof, into an annular duct in a further end space, left between the said other axial end face and the end flange adjacent thereto.

13 A method as claimed in claim 12, wherein an annular body is provided, around the central axial portion, in the space left between the said other axial end face and the end flange adjacent thereto so that the annular duct in that space is defined between the annular body therein and the end flange concerned, which annular body is formed with axial ducts through which impregnating agent passes from the coil winding assembly to the said annular duct.

14 A method as claimed in claim 1, 12 or 13, wherein the or each said annular body is formed from a perforated plate.

15 A method as claimed in claim 1, 12, 13 or 14, wherein the or each said annular body has supporting projections which bear on the adjacent end flange.

16 A method as claimed in any one of claims 1, and 12 to 15, wherein the or each said axial end face is covered by a layer of electrical insulating material permeable by the impregnating agent.

17 A method as claimed in any one of claims 12 to 15, wherein the or each said annular body bears directly on a layer of electrical insulating material that is permeable by the impregnating agent and covers the said axial end face that is adjacent to the annular body concerned.

18 A method as claimed in any one of claims 1, and 12 to 17, wherein the said central axial portion has the form of a hollow cylinder and the said end flanges are circular in form 70 19 A method as claimed in any one of claims 1 and 12 to 18, wherein the coil winding assembly comprises superconductor windings of Nb 3 Sn, or V 3 Ga, formed "in situ" by heat treatment 75 A method of manufacturing a superconductor coil, substantially as hereinbefore described with reference to the accompanying drawing.

HASELTINE, LAKE & CO, Chartered Patent Agents, Hazlitt House, 28 Southampton Buildings, Chancery Lane, London, WC 2 A 1 AT.

Also Temple Gate House, Temple Gate, Bristol, B 51 6 PT.

And 9 Park Square, Leeds, L 51 2 LH, Yorks.

Printed for Her Majesty's Stationery Office.

by Croydon Printing Company Limited Croydon Surrey 1981.

Published by The Patent Office 25 Southampton Buildings.

London, WC 2 A I AY, from which copies may be obtained.

1 593 923